The detailed examination of humus soils of various kinds is becoming of increasing importance in view of the schemes now on foot for the reclamation of much heath and moor land. One of the most important things to establish has seemed to the authors to be the amount of nitrogen existing in the form of ammonia or of ammonium compounds, as it is possible that a knowledge of this figure might form a basis for a more scientific classification of soil organic matter than at present exists.

Gill in 1871 first pointed out that when an excess of basic lead acetate is added to a solution of invert sugar the negative rotation of the latter is greatly reduced owing to the formation of a soluble lead compound of laevulose. If sufficient lead solution is added the negative rotation may become a positive one; thus in one experiment quoted by Gill a negative reading of – 28° was transformed into a positive value of + 57°. The change of rotation was not, however, permanent and on removing the lead or on acidifying the solution the original rotatory power was restored. The change of rotation was attributed to an effect of the lead on the laevulose only; a solution of dextrose was practically unaffected by the presence of basic lead acetate. Since Gill's paper the effect of basic lead acetate as a source of error in sugar analysis has been the subject of numerous papers especially by Pellet, Svoboda, Edson, Prinsen Geerligs, Watts and Tempany and Eynon.

The present work has been undertaken with the object of ascertaining the actual compounds of phosphoric acid and lime present in rock phosphates, a better knowledge of these compounds being of some agricultural importance.

(1) Grassland has been classified as natural and semi-natural; both classes have been further sub-divided according to the botanical composition of the herbage in relation to habitat (pp. 27–36).

(2) The plants which colonise natural grasslands have been called primary indigenous species; and those which come in without being sown and contribute largely to the herbage on semi-natural types have been designated secondary indigenous species (p. 37).

Few reactions are more important to the soil chemist than that involved in the action of dilute acids on the phosphorus compounds of the soil, but, owing to its complex nature, little has been definitely ascertained about it. The importance of the reaction lies in the fact that it affords a distinction between those phosphorus compounds which are fairly easily soluble, and may therefore be expected to enter the plant root without much difficulty, and the less soluble compounds which are of less value in the nutrition of plants.

It has been known from the earliest times that soils would remove salts and colouring matters from solution and the problems arising out of the observations made on this phenomenon were among the earliest to be attacked by agricultural chemists. It was known to Aristotle that sea water lost some of its taste by filtration through sand and this observation seems to have been confirmed and applied in many ways. Lord Bacon in his Sylva Sylvarum discussed the question of making sea water potable by filtering through sand. Le Comte de Marsilli made quantitative experiments. Sea water was filtered through fifteen successive vessels of garden soil and a diminution in the salt content was proved by evaporation and by the change in specific gravity. Similar results were obtained with sand. Boyle Godfrey discussed the question of making sea water fit for use on ships and observed that if sea water be put into a stone straining cistern the first pint that runs through will be like pure water, having no taste of salt, but the next pint will be as salt as usual. Stephen Hales in dealing with the same question refers to the use of a soft stone by the Dutch as a filtering material, but he points out that this method has no practical value as only the first portions of the filtrate are free from salt.

Points of considerable interest, both scientific and practical, are raised by the question as to whether a tree which fruits exceptionally well as compared with its fellows in one season, will tend to fruit exceptionally well, or the reverse, in the following season. We know of no definite reason why the behaviour of a tree as regards fruiting should alternate in consecutive years, and no such behaviour has been observed in the case of animals. Its doing so would imply that fruiting is due to the gradual accumulation of some substance in the tree, which becomes exhausted whenever heavy bearing occurs, and that the stock of this substance does not become properly replenished till after another season has elapsed. This is quite possible, but quite unproven. Indeed it seems to be actually opposed to the well established fact that growth and fruiting are antagonistic to each other; for the exceptionally feeble growth which accompanies exceptionally heavy cropping, must tend, as all restriction of growth does, to the formation of an increased number of blossom-buds for the following season, and probably, therefore, to heavy cropping also, during that following season; unless of course, the cropping has been so heavy as to seriously impair the vigour of the tree; but this is an excessive condition which need not be considered here. We might also expect similar behaviour as regards fruiting in consecutive years, on the general grounds that individual trees must differ from each other in fertility, as in every other respect. On the other hand, there is a strong belief amongst horticulturists that a tendency to alternate fruiting, as it may conveniently be termed, does really exist; so much so, that the recommendation is often made, to severely thin the fruit from a tree which is bearing heavily, with the object of destroying this tendency, and of obtaining moderate and more uniform bearing in future years.

1. When salts or minerals containing phosphoric acid are ignited with ammonium fluoride as in the ordinary process of analysis of silicates, considerable loss of the phosphoric acid may occur. It is probable that the phosphorus is volatilised in the form of a phosphorus fluoride.

2. The loss is least in the case of salts containing an alkali metal. It is less in the case of disodium hydrogen phosphate than in that of potassium dihydrogen phosphate, and is greatest in the case of phosphates of the alkali earth metals, such as calcium phosphate or apatite.